Light Emitting Diodes (LEDs) are desirable for use in lighting fixtures due to the efficiency and reliability of LEDs. LEDs used for interior lighting are typically high output devices that emit light that is a “pure” white (or nearly white) color. This color and output level work well for situations where bright lighting is desired. Some modern LED interior lights have a dimming feature for when lower light levels are desired. However, the color of an LED does not change appreciably when the LED is dimmed, as does an incandescent light.
Unlike LEDs, traditional incandescent bulbs change color as they dim. Normally, the filament in an incandescent bulb emits a light with a color temperature of about 3000 Kelvin (K) at full brightness, which is considered a “white” color. As the incandescent light is dimmed and the current is decreased, the filament emits a light that shifts away from “white” toward a more red/amber color output (e.g., a lower color temperature).
The color or appearance of a light source can be defined as a color temperature and is measured in degrees Kelvin (K). For example, a fluorescent light may have a very “cold” color temperature of 4000K (which may appear bluish), whereas a standard incandescent light bulb may have a “cool” color temperature of about 3000K (appears white) at full brightness. Further, a standard bulb may have a “warm” color temperature of 2000K (appears amber/red) when dimmed to 5-10% of full brightness. The color temperature change of an incandescent light bulb generally follows the color change of a cooling black body (i.e., the Black Body Locus). People sometimes prefer this “warming” effect and dislike the non-color shifting dimming of LED lights.
Therefore, what is desired is a lighting system suitable for LED lights which mimics the color curve of an incandescent light when dimming.
An object of the present invention is to provide an LED lighting fixture which mimics the warming color change of an incandescent bulb when the lighting fixture is dimmed.
Another object of the invention is to provide an LED lighting fixture with the above features and which provides a precise, “cool” light color that approaches a “white” light source when at full brightness.
Another object of the invention is to provide an LED lighting fixture having the above features and having the ability to dim in a smooth, gradual manner, without perceptible discrete steps or jumps in the level of light during dimming.
Another object of the invention is to provide an LED lighting fixture having the above features and having the ability to dim in a smooth, gradual manner, without perceptible, discrete steps or jumps in the color of light during dimming.
Another object of the invention is to provide an LED lighting fixture having the above features which is operable with standard drivers for LED lighting fixtures.
Still another object of the invention is to provide an LED lighting system that provides for LED dimming along with perceived LED color shifting that mimics a standard incandescent lamp that is dimmable for substantially the entire range of a commercially available dimmer switch.